The invention relates to an apparatus for controlling the delivery of medical fluids to a patient.
In determining the proper dosage of medical fluids, closed-loop control circuits are used to set a defined depth of hypnosis, analgesia, or degree of relaxation. As dosage devices, syringe pumps with which the medical fluids can be delivered to the patient are known. The resultant medical fluid concentration, such as the enrichment of medical fluid in the blood plasma, can be determined only by drawing blood and then examining it. In conjunction with certain medications, so-called patient models have therefore been developed, with which the medical fluid enrichment in the blood plasma can be simulated mathematically. The patient models that have been known until now apply only in conjunction with the medications associated with them and have been validated by extensive patient studies and approved by the appropriate authorities.
The so-called 3-compartment model is currently the standard patient model for the pharmacokinetics of intravenous anesthetics. It comprises one central compartment and two peripheral compartments. The division into three compartments is based on the following thought: If one begins at a single volume into which an anesthetic is applied, then two quantity courses can be determined, that is, the current quantity of anesthetic in that volume, and the quantity cumulatively eliminated from it. However, in nearly all anesthetics, the total of these two quantities does not represent the administered dose; instead, there is always a missing quantity. To compensate for this, a further peripheral volume is introduced.
One apparatus for automatic delivery of a medical fluid to a patient is known from European Patent Disclosure EP 1 136 090 A2.
The dosage rate of the medical fluid is processed in a patient model, which receives the appropriate medical fluid data from a medication database. The patient model calculates the medical fluid concentration in the body of the patient from past values for the medical fluid delivery. The calculated medical fluid concentration is compared with a set-point concentration and is supplied as a difference to a concentration regulator. The control input for the medical fluid concentration is furnished by a further regulating part, which processes a derived variable in the form of a body effect to be set (pharmacodynamics).
For monitoring the manual administration of medical fluids, the therapeutic range of the medical fluid delivery is monitored. For this purpose, it is ascertained whether the medical fluid concentration established does not exceed a predetermined tolerance range. It is left to the user how to react to any exceeding of the limit value.
For monitoring closed-loop control circuits, it is known to measure the system state with a second sensor, independent of the closed-loop control circuit, and to assess the measurement signals in a separate monitoring channel. However, a further sensor entails additional expense and, because it means a further cable connection, makes provisions for patient therapy more difficult. For the subject matter addressed here, moreover, there is no known sensor or measurement principle with which the medical fluid concentration could be determined directly in the patient's body.